ASME PCC-1 Appendix O gives a joint component approach to assessing the assembly stud stress for a flanged joint. It states the minimum permissible bolt stress must be selected by the user and then goes on to say its typically in the range of 20-40% of ambient bolt yield stress. My employer has guidelines which roughly translate to 30% and for the most part we don't need to think too much about this minimum value as it's rarely the governing factor in leakage modelling, however, on the rare occasion it is I've found very little literature defining the pitfalls of low assembly stud stress.
Issues that I've come across or read which may ultimately result in leaks include the following:
[ul]
[li]co-efficient of friction tests have shown a wider standard deviation of results at low assembly stresses so application of load is less accurate than at higher assembly stresses (assembly by torque)[/li]
[li]overall joint relaxation is more pronounced at lower assembly loads [/li]
[/ul]
I'd appreciate any input with regards to other concerns of low assembly stud stress. And if people know of any literature, codes, papers that discuss this issue I'd love to know about them.
Note that I've deliberately left out the obvious one of ultimately applying low gasket stress but please assume that sufficient gasket stress is applied.
Apologies if this has been asked before, I've looked but can't find any threads answering my query.
Issues that I've come across or read which may ultimately result in leaks include the following:
[ul]
[li]co-efficient of friction tests have shown a wider standard deviation of results at low assembly stresses so application of load is less accurate than at higher assembly stresses (assembly by torque)[/li]
[li]overall joint relaxation is more pronounced at lower assembly loads [/li]
[/ul]
I'd appreciate any input with regards to other concerns of low assembly stud stress. And if people know of any literature, codes, papers that discuss this issue I'd love to know about them.
Note that I've deliberately left out the obvious one of ultimately applying low gasket stress but please assume that sufficient gasket stress is applied.
Apologies if this has been asked before, I've looked but can't find any threads answering my query.
